For an average passenger car about 250 different blanks are needed. The blanks have to be cut of sheet metal coils. De-pending on the shape complexity, this can be done by swivel-mounted shears for angular straight cuts, adjustable dies with variable pitch for parallel cuts, or by form dies for blanks with a complicated contour. By use of form dies and appropriate nesting on the coil material usage can be minimized. However, tooling costs increase and are not justified for simple shapes. Typically 50-70 of the total 250 parts will be cut by form dies.
In principle, the blank follows the binder contour of the press tool as it was designed by die systems engineering. However, material flow rate is not equally distributed along the binder due to dynamic effects, material properties and process parameters. Lock beads may be inserted to avoid folds and to influence material hardness. Therefore, the binder geometry is insufficient to determine the shape of the form dies for blank cutting. Although soft tooling experiments and FEM computations can help in predicting the blank contour, only tool tryout will deliver conclusive results.
During the blank engineering process for a new car line, the manually optimized shape has to be digitized for tool construction and blank nesting. Since the sheet metal is two-dimensional the digitization task is not complicated in terms of technology used. The critical factor is time needed to digitize the 50-70 parts that require form dies. In the state of the art, the following techniques are used for this task:                coordinate measuring machine (CMM),        paper copy and digitization device, and        paper copy and manual measurement (re-engineering).        
These techniques are inherently slow. The accuracy of CMMs is higher than adequate for this task. Since they are not provided for such relatively low precision work they will often not be available. Even so, the 3D point data of a CMM has to be converted into a preferred CAD format. The start point of the two other methods is a paper copy of the blank. The out-line of the blank is simply transferred by a pencil on a large sheet of paper. In a second step a drawing table with a built-in electronic digitization device can be used. Points on the contour can be picked and digitized by pressing a trigger button. Again, this data has to be converted into the preferred CAD drawing format. As an alternative, the paper sketch of the blank can be used for part re-engineering. Part dimensions can be measured by hand on paper and are then keyed in a 2D drawing program to reconstruct the blank.
Equipment such as drawing tables has disappeared with the introduction of CAD and closed-loop CAD/CAM environments and is only available through external services. The access to external suppliers will additionally slow down the process.
Taking the mentioned drawbacks of current state of the art into account, the objective of the present invention was to achieve cost reductions and an improved timing in the production of sheet metals for cars.